The Court’s June 25, 2012 decision in Arizona v. United States struck down three of the four challenged sections of Arizona’s “Support Our Law Enforcement and Safe Neighborhoods Act,” colloquially known simply as “S.B. 1070.” Two of these provisions created state crimes to punish immigrants for not carrying federally required registration documents and for seeking work without authorization; the third provision expanded state arrest authority to allow police to arrest suspected immigration violators. The Court held that these legislative efforts were preempted by comprehensive federal regulation of immigration enforcement. The Court additionally left open the possibility that the fourth challenged provision of S.B. 1070, requiring Arizona police officers to run immigration status checks on suspected immigration violators, might be held unconstitutional or preempted, depending on how the law is actually applied.

This Article explores a less obvious consequence of Arizona: its implications for the continuing viability of a critical federal enforcement mechanism, the immigration detainer. The Arizona decision saps the vitality out of this mechanism, and exposes it as far exceeding any Congressional grant of authority and as conflicting with the Fourth Amendment principles discussed in the opinion.

I begin in Part II with a discussion of the context in which S.B. 1070 was passed, a brief history of the litigation over S.B. 1070, and the Arizona decision. The ongoing civil rights battle over immigration brought to the fore issues of racial profiling and the debate over whether states possess “inherent authority” to enforce the immigration laws. Arizona failed to put these issues to rest and the Court’s silence ensures ongoing controversy and litigation. Digesting the Arizona opinion, I address in turn: (1) the majority’s preemption analysis (and its failure to address the civil rights issues) with respect to the four challenged provisions of S.B. 1070; (2) the Fourth Amendment discussion among the Justices, attendant to the question of whether state officials may subject suspected immigration violators to prolonged detention; and (3) the omission by the Justices — except for Justice Scalia — of any discussion of a state’s “inherent authority” or police power with respect to immigration enforcement.

The remainder of the Article assesses the effect Arizona will have on the federal government’s use of immigration detainers to obtain custody over prisoners held by other law enforcement agencies. Ironically, while Arizona trumpets the supremacy of the federal government in the field of immigration, the opinion has negative implications for the federal government’s central enforcement mechanism for obtaining custody of suspected immigration violators. The legality of the immigration detainer system put in place by the executive branch can be analyzed through the same doctrinal frames seen in Arizona — preemption and the Fourth Amendment concerns with prolonged detention.

I proceed to that analysis in Part III, addressing Arizona’s impact on federal authority to issue immigration detainers requiring other law enforcement officials to prolong the detention of their prisoners. I conclude that the detainer regulation purporting to allow this is ultra vires for the same reason the Arizona Court held parts of S.B. 1070 preempted — the executive branch’s detainer regulation is flatly inconsistent with the comprehensive enforcement regime established by Congress. Additionally, there are substantial Fourth Amendment problems with the immigration detainer regulation that are illuminated by the Fourth Amendment discussion in Arizona. The regulation is invalid because of these substantial constitutional questions.